가려움은 임상의가 빈번하게 마주하는 흔하고 비특이적인 증상으로 삶의 질 저하와 밀접하게 연관되어 있다. 가려움은 말초에서 염증반응, 물리적 자극, 항원 노출 등에 의해 시작되며, 다양한 매개물질과 감각신호전달 경로를 통해 시상과 대뇌피질로 전달되어 가려움이라는 자극을 느끼게 된다.
병적인 가려움을 일으키는 질환들은 크게 (1) 피부과적 질환, (2) 내과적 질환에 동반되는 가려움, (3) 신경병적 가려움, (4) 심인성 가려움의 4가지로 분류된다. 가려움을 호소하는 환자가 있다면 우선 정확한 병력청취와 피부병변 유무에 대한 검진이 필요하며, 동반된 내과적 질환 유무에 대한 평가를 위해 검사를 시행하여 감별 진단을 해야 한다. 가려움은 기간에 따라서 분류하기도 하는데, 6주 이상 지속될 때 만성 가려움으로 간주한다. 급성 가려움과 두드러기는 주로 히스타민 작용에 의해 발생하므로 항히스타민제 투여가 치료의 근간이 된다. 반면 만성 가려움을 일으키는 대부분의 질환의 경우 히스타민과 연관성이 없으며 원인 질환에 따른 맞춤 치료가 필요하다(Table 6, Fig. 2).
가려움의 치료에는 국소요법과 전신요법이 있으며, 가려움을 일으키는 기전에 대한 연구가 진행됨에 따라 치료법도 다양해지고 있다. 증상이 경한 경우에는 보습과 국소 도포제를 사용해 볼 수 있고, 증상이 심하거나 만성적으로 지속될 경우 전신치료법을 고려 할 수 있다. 흔히 가려움 치료제로 알려져 있는 항히스타민제 외 신경계 작용 약물, 면역조절제와 표적치료제가 임상에서 사용되고 있다. 향후 가려움의 발생기전에 대한 이해가 발전됨에 따라 “가렵다” 라는 비특이적인 증상에 대해 개별화된 치료법 개발을 기대해 본다.

“Itch” is an unpleasant sensation that elicits a desire to scratch. It is a common complaint among many patients and is associated with a markedly reduced quality of life. The pathogenesis of itch begins with various pruritogens stimulating free nerve endings in the skin, which causes an itch signal to travel through the spinothalamic tract to the brain where the sensation is processed. Scratch-ing an itch initially activates the reward systems in the midbrain and striatum, and this positive reinforcement leads to the repetitive scratching behavior that damages the skin barrier. Mediators such as histamine, serotonin and cytokines are released from the dam-aged skin, which further aggravates the itch and initiates a vicious “itch-scratch cycle.” Such processes may eventually lead to neural sensitization, where weaker stimuli can cause a more severe pruritic sensation. Chronic itch is one that lasts beyond 6 weeks. Patho-logic pruritus can be classified into four different categories based on its cause: dermatologic, systemic, neuropathic, and psycho-genic itch. Regardless of the cause, antihistamines are often prescribed as a first-line treatment of chronic itch, but more often than not they prove to be ineffective in bringing symptom relief. Both topical and systemic therapies are used to treat itch, and adequate treatment selection is considered according to symptom severity and chronicity. As the pathogenesis of itch becomes elucidated, more exciting new therapeutic options targeting pruritogenic mediators are becoming increasingly available. This review provides an overview of the pathophysiology, causes and the treatment of chronic itch. (Allergy Asthma Respir Dis 2021;9:189-202)

Allergic rhinitis (AR) is one of the most common allergic diseases characterized by stuffy nose, rhinorrhea, sneezing, and itching. Re-searchers have indicated an increase in the prevalence of AR and younger-age onset during the last few decades. The increasing burden of AR has caused many researchers to investigate time trends of the prevalence of AR and to identify its risk factors. The most commonly used epidemiological studies are cross-sectional ones such as the International Study of Asthma and Allergies in Childhood study and big data from National Health Insurance Service or National Health and Nutrition Examination Survey. How-ever, these studies have many limitations including recall bias, selection bias, and deficit of objective evaluation. Furthermore, cross- sectional studies cannot reflect new risk factors associated with the development of AR. New epidemiological studies will be needed to cover genetic factors, environmental changes, microbiomes, and lifestyles that are known to be risk factors for AR. Fur-ther studies will be needed to determine the prevalence, natural history, and risk factors of AR in order to advance our understand-ing of the pathophysiology, prevention, and management of comorbidities of AR. (Allergy Asthma Respir Dis 2021;9:203-207)

Purpose: Allergen sensitization is constantly changing, and understanding these changes can help manage and prevent allergic diseases. This research analyzed and compared the changes in allergen sensitization in children diagnosed with allergic diseases us-ing the skin test and the multiple allergen simultaneous test.
Methods: We retrospectively analyzed the data on children who were diagnosed with allergic diseases and received immunother-apy at Yonsei Medical Center from 1980 to 1998 and they were screened for allergen sensitization at Severance Hospital from 2005 to 2019.
Results: Between 1980 and 1998, and between 2005 and 2019, data on 3,205 (male, 70.3%; mean age, 7.2±2.9 years) and 15,318 children (male, 62.8%; mean age, 8.8±4.5 years) were analyzed. The sensitized allergens that appeared in the 1980-1998 included Dermatophagoides farinae (91.0%), Dermatophagoides pteronyssinus (76.3%), cockroach (13.5%), and Alternaria (11.5%), in order of frequency; further, the sensitized allergens that appeared in the 2005-2019 included D. farinae (45.0%), D. pteronyssinus (39.6%), cat dander (12.2%), and dog dander (9.1%), in order of frequency. D. farinae and D. pteronyssinus demonstrated the highest sensitization rates, although the rates decreased gradually. The sensitization to cat dander and dog dander showed a growing trend, and sensiti-zation to Humulus japonicus, Candida, and cockroach decreased after 2005.
Conclusion: Over the past 40 years, the allergen sensitization in Korean children with allergic diseases has increased. These changes reflect lifestyle and environmental changes and influence allergic disease management approaches. Thus, changes in allergic sensi-tization should be monitored continuously. (Allergy Asthma Respir Dis 2021;9:208-215)

Purpose: Sleep-disordered breathing is one of the complicating characteristics in patients with Prader-Willi syndrome (PWS). No de-tailed description and risk factors are suggested on breathing problems during sleep in Korean children with PWS.
Methods: We reviewed clinical and sleep-study data in patients with PWS who underwent polysomnography before they took the growth hormone therapy.
Results: Of the 27 patients with PWS, 25 (92.6%) had sleep-disordered breathing, of whom 14 showed moderate to severe sleep ap-nea. Obstructive dominance was prevalent (64%), followed by central dominance (24%). The apnea-hypopnea index (AHI) increased with increasing weight-for-height z-score (WHZ) (r=0.50, P=0.009), but did not differ by age. Apnea duration of over 12 months was longer in the patient group than in the infant group (15.1±4.3 seconds vs. 9.4±1.7 seconds, P=0.001) and in the obese than non- obese groups (16.8±4.3 seconds vs. 10.0±2.0 seconds, P=0.003). Desaturation below 70% was more common in the obese than nonobese subjects (3/9 vs. 0/18, P=0.029). Age was not different between the central and obstructive apnea groups, but patients with central apnea tended to be younger than patients with obstructive apnea (median [range]: 8.0 months [6.0-12.0 months] vs. 16.5 months [8.5-79.5 months], P=0.092). In addition, patients with obstructive apnea showed higher AHI (12.8 [5.9-19.2] vs. 3.9 [3.4-4.5], P=0.045).
Conclusion: Sleep-disordered breathing is common in PWS children with different intensity and patterns according to age and BMI. Close monitoring of breathing problems during sleep is required in PWS patients. (Allergy Asthma Respir Dis 2021;9:216-224)

Purpose: Adverse transfusion reactions (ATRs) are unfavorable reactions to the transfused unit, and the severity may be different among individuals, depending upon the type of reactions and the patient's susceptibility. It is necessary to operate and manage a systematic monitoring system to minimize these ATRs and increase the safety. This study was conducted to evaluate clinical features of transfusion-related adverse events and morbidities.
Methods: We retrospectively analyzed transfusion data from electronic medical records during the recent 3 years (April 2017 to April 2020) at Seoul National University Bundang Hospital. The electronic search strategy was applied to search for the type of blood prod-ucts prescribed and identify symptoms that occurred during transfusion as recorded in the nursing chart which is based on the In-ternational Classification for Nursing Practice.
Results: A total of 18,772 people were transfused during the study period. A total of 524 people were reported as suspected ATRs, of whom 466 were finally confirmed. Red blood cell was the most frequent culprit blood product (59.9%), followed by apheresis plate-let (25.1%), fresh frozen plasma (10.1%), and platelet (4.9%). Clinical symptoms included fever (54.9%), urticaria and itching (34.7%), chillness and shivering (21.9%), and chest discomfort (6.0%), dyspnea (5.3%), cold sweating (3.8%), hypotension (2.1%), and palpita-tions (1.9%). The severity of ATRs were mild (91.8%), moderate (7.1%), and severe (1.1%).
Conclusion: ATRs are mostly mild, but life-threatening reactions may occur. Physicians should be aware of various features of ATRs to appropriately recognize and treat such patients. (Allergy Asthma Respir Dis 2021;9:225-230)

Purpose: Cluster analysis on pediatric asthma identifying a cluster characterized by obesity, females, and puberty showed that obe-sity is an independent risk factor for severe asthma in this cluster. In the present study, we aimed to investigate the effect of over-weight/obesity on lung function and asthma severity in prepubertal asthmatic children.
Methods: One hundred fifty-five prepubertal children (aged 6-10) with asthma were enrolled and divided into 2 groups: the over-weight/obese group (body mass index [BMI] ≥85th percentile, n=44) and the normal BMI group (<85th percentile, n=111). We re-viewed their medical records and analyzed whether there were any differences in clinical features, lung function and degree of bron-chial hyperresponsiveness (BHR) between the 2 groups. The clinical factors associated with asthma severity were also investigated.
Results: There was no difference in clinical features between the 2 groups. Pulmonary function tests showed that only forced vital capacity in 1 second/forced vital capacity (FEV1/FVC) was significantly lower in the overweight/obese group than in the normal BMI group (P=0.032). There was no difference in dysanapsis and BHR between the 2 groups. There were significantly more children with moderate-to-severe asthma in the overweight/obese group compared to the normal BMI group (P=0.018). In multivariate logistic regression analysis, overweight/obesity has been identified as an independent risk factor of affecting asthma severity (odds ratio, 2.44; P=0.018), in addition to the already known risk factor, FEV1.
Conclusion: Our study showed that overweight/obese prepubertal asthmatic children had lower FEV1/FVC than those with normal BMI. It also suggests that overweight/obesity may be an independent risk factor for severe asthma before puberty. (Allergy Asthma Respir Dis 2021;9:231-237)

Purpose: Acute asthma exacerbations in children have seasonal variations and occur frequently in fall. Respiratory viral infections and environmental allergens are associated with asthma exacerbation. This study aimed to identify seasonal trends of asthma exac-erbation and the effects of respiratory viral infection and allergen sensitization on the seasonality of asthma exacerbation in children.
Methods: Children under the age of 18 years who visited to the Emergency Department or hospitalized for acute asthma exacerba-tions from 2011 to 2019 were included. We reviewed medical records, including demographics, date of asthma exacerbation, results of respiratory virus and allergen sensitization, and they were analyzed to identify the seasonal trends of asthma exacerbation.
Results: A total of 320 asthma exacerbations were included, with the highest frequency in fall. Human rhinovirus was positive in 64.7% and 60.0% in fall and spring exacerbations, respectively. House dust mite sensitization was highest in fall at 78.5%, while food sensitization was highest in spring at 76.9%. In patients who were sensitized to house dust mites or food allergens, respiratory viral infections further increased asthma exacerbation in fall and spring, respectively.
Conclusion: Respiratory virus may be associated with asthma exacerbation in fall and spring. House dust mite and food sensitiza-tions may be associated with fall and spring asthma exacerbations by worsening the severity of asthma symptoms caused by respi-ratory viral infections. In childhood asthmatic patients with allergen sensitization, avoidance of sensitized allergens, prevention of viral infection, and more active treatment of viral infection may help prevent acute asthma exacerbations. (Allergy Asthma Respir Dis 2021;9:238-244)

Anaphylaxis is an acute serious systemic allergic reaction that can lead to death, requiring immediate diagnosis and treatment. In particular, food is the most common cause in children, adolescents, and young adults. In addition to physical contact between food and skin, anaphylaxis can also be induced by exposure other than ingestion, such as inhalation of aerosolized food proteins. Korean males undergo medical screening prior to a compulsory military service. A history of possible food allergy requires referral to a spe-cialized allergy clinic. A 19-year-old male patient enlisted in the military was referred to the allergy clinic for an oral provocation test. It was confirmed that anaphylaxis was caused not only by walnut intake, but also by skin contact or by inhaling walnut particles. We report the case with the literature review. (Allergy Asthma Respir Dis 2021;9:245-248)

Rapid-onset obesity with hypoventilation, hypothalamic, and autonomic dysregulation (ROHHAD) syndrome is a rare disease char-acterized by rapid progression of obesity and central hypoventilation with autonomic and endocrine dysregulation. There is no gold-standard diagnostic method for ROHHAD syndrome; it is diagnosed based on a years-long clinical course. For this reason, di-agnosis of ROHHAD syndrome is often delayed. In particular, ROHHAD has a high mortality rate due to cardiopulmonary arrest when quick diagnosis and appropriate intervention of central sleep apnea are not timely. We report a case in which an 11-year-old girl with central sleep apnea was diagnosed with ROHHAD syndrome: the clinical course with early breathing intervention using noninvasive positive pressure ventilation. We emphasize the importance of respiratory interventions in the clinical course of RO-HHAD syndrome. (Allergy Asthma Respir Dis 2021;9:249-254)